1. Field of the Invention
The present invention relates to a reversible pump having an improved structure such that intake fluid is selectively discharged in two directions, and a system for supplying developer in a liquid electrophotographic printer using the same.
2. Description of the Related Art
In general, liquid electrophotographic printers print desired images by developing electrostatic latent images, formed on a photoreceptor medium such as a photoreceptor belt, using a developer of a predetermined color and transcribing the resultant images on paper.
As shown in FIG. 1, the liquid electrophotographic printer is comprised of a developing unit 20 for supplying a developer to a photoreceptor belt 10 and developing the photoreceptor belt 10, and a developer supply system for continuously supplying a developer of a predetermined concentration to the developing unit 20.
The developer supply system includes a developer tank 30 for containing a developer of a concentration suitable for developing, a spray nozzle 60 for supplying the developer to the photoreceptor belt 10 and the developing unit 20, and a supply pump 40 for pumping the developer from the developer tank 30 to the spray nozzle 60. The developer contained in the developer tank 30 is a diluted solution where concentrated ink including powder toner and liquid carrier are mixed in a predetermined ratio. Thus, in order to prevent the concentration of the developer from becoming non-uniform since the toner settles at the bottom of the developer tank 30, a valve 50 is installed between the supply pump 40 and the spray nozzle 60 in the developer supplying system to return the developer to the developer tank 30 and agitate the developer within the developer tank 30. That is, the valve 50 operates so that the developer contained in the developer tank 30 is pumped by the supply pump 40 and supplied to the developing unit 20 via the spray nozzle 60, and that the developer pumped by the supply pump 40 returns to the developer tank 30 in a standby state after the developing operation is completed.
As shown in FIGS. 2 and 3, the supply pump 40 includes an impeller 41 rotatably installed within a case 45 having an intake 42 and an outlet 43, a motor 44 for rotating the impeller 41, and a plurality of blades 41 a installed on the impeller 41. In the supply pump 40 having this general structure, fluid taken in through the intake 42 is discharged through the outlet 43 as the impeller 41 rotates in the direction indicated by an arrow.
However, the conventional supply pump 40 can perform only two operations such as discharge or suspension of fluid according to the driving of the motor 44. Thus, an expensive valve 50 must be installed as described above to supply the developer within the developer tank 30 to the developing unit 20 or return the same to the developer tank 30. Accordingly, in a printer for realizing a plurality of colors such as a color laser printer, a valve must be installed for the developing unit of each color, thereby increasing the number of component parts to be managed. Therefore, a pump having a structure which can realize a plurality of fluid discharging paths without adopting an expensive valve is required.